Vitamin B6 depletion in man: urinary excretion of quinolinic acid and niacin metabolites

States of quinolinic acid excess in urine: A systematic review of human studies

Introduction

Quinolinic acid is an intermediate compound derived from the metabolism of dietary tryptophan. Its accumulation has been reported in patients suffering a broad spectrum of diseases and conditions. In this manuscript, we present the results of a systematic review of research studies assessing urinary quinolinic acid in health and disease.

Methods

We performed a literature review using PubMed, Cochrane, and Scopus databases of all studies reporting data on urinary quinolinic acid in human subjects from December 1949 to January 2022.

Results

Fifty-seven articles met the inclusion criteria. In most of the reported studies, compared to the control group, quinolinic acid was shown to be at increased concentration in urine of patients suffering from different diseases and conditions. This metabolite was also demonstrated to correlate with the severity of certain diseases including juvenile idiopathic inflammatory myopathies, graft vs. host disease, autism spectrum disorder, and prostate cancer. In critically ill patients, elevated quinolinic acid in urine predicted a spectrum of adverse outcomes including hospital mortality.

Conclusion

Quinolinic acid has been implicated in the pathophysiology of multiple conditions. Its urinary accumulation appears to be a feature of acute physiological stress and several chronic diseases. The exact significance of these findings is still under investigation, and further studies are needed to reveal the subsequent implications of this accumulation.

Multiple roles of haem in cystathionine β-synthase activity: implications for hemin and other therapies of acute hepatic porphyria

The role of haem in the activity of cystathionine β-synthase (CBS) is reviewed and a hypothesis postulating multiple effects of haem on enzyme activity under conditions of haem excess or deficiency is proposed, with implications for some therapies of acute hepatic porphyrias. CBS utilises both haem and pyridoxal 5′-phosphate (PLP) as cofactors. Although haem does not participate directly in the catalytic process, it is vital for PLP binding to the enzyme and potentially also for CBS stability. Haem deficiency can therefore undermine CBS activity by impairing PLP binding and facilitating CBS degradation. Excess haem can also impair CBS activity by inhibiting it via CO resulting from haem induction of haem oxygenase 1 (HO 1), and by induction of a functional vitamin B₆ deficiency following activation of hepatic tryptophan 2,3-dioxygenase (TDO) and subsequent utilisation of PLP by enhanced kynurenine aminotransferase (KAT) and kynureninase (Kynase) activities. CBS inhibition results in accumulation of the cardiovascular risk factor homocysteine (Hcy) and evidence is emerging for plasma Hcy elevation in patients with acute hepatic porphyrias. Decreased CBS activity may also induce a proinflammatory state, inhibit expression of haem oxygenase and activate the extrahepatic kynurenine pathway (KP) thereby further contributing to the Hcy elevation. The hypothesis predicts likely changes in CBS activity and plasma Hcy levels in untreated hepatic porphyria patients and in those receiving hemin or certain gene-based therapies. In the present review, these aspects are discussed, means of testing the hypothesis in preclinical experimental settings and porphyric patients are suggested and potential nutritional and other therapies are proposed.

Metabolite profile analysis reveals functional effects of 28-day vitamin B-6 restriction on one-carbon metabolism and tryptophan catabolic pathways in healthy men and women

Suboptimal vitamin B-6 status, as reflected by low plasma pyridoxal 5'-phosphate (PLP) concentration, is associated with increased risk of vascular disease. PLP plays many roles, including in one-carbon metabolism for the acquisition and transfer of carbon units and in the transsulfuration pathway. PLP also serves as a coenzyme in the catabolism of tryptophan. We hypothesize that the pattern of these metabolites can provide information reflecting the functional impact of marginal vitamin B-6 deficiency. We report here the concentration of major constituents of one-carbon metabolic processes and the tryptophan catabolic pathway in plasma from 23 healthy men and women before and after a 28-d controlled dietary vitamin B-6 restriction (<0.35 mg/d). liquid chromatography-tandem mass spectrometry analysis of the compounds relevant to one-carbon metabolism showed that vitamin B-6 restriction yielded increased cystathionine (53% pre- and 76% postprandial; P < 0.0001) and serine (12% preprandial; P < 0.05), and lower creatine (40% pre- and postprandial; P < 0.0001), creatinine (9% postprandial; P < 0.05), and dimethylglycine (16% postprandial; P < 0.05) relative to the vitamin B-6-adequate state. In the tryptophan pathway, vitamin B-6 restriction yielded lower kynurenic acid (22% pre- and 20% postprandial; P < 0.01) and higher 3-hydroxykynurenine (39% pre- and 34% postprandial; P < 0.01). Multivariate ANOVA analysis showed a significant global effect of vitamin B-6 restriction and multilevel partial least squares-discriminant analysis supported this conclusion. Thus, plasma concentrations of creatine, cystathionine, kynurenic acid, and 3-hydroxykynurenine jointly reveal effects of vitamin B-6 restriction on the profiles of one-carbon and tryptophan metabolites and serve as biomarkers of functional effects of marginal vitamin B-6 deficiency.

A mathematical model of tryptophan metabolism via the kynurenine pathway provides insights into the effects of vitamin B-6 deficiency, tryptophan loading, and induction of tryptophan 2,3-dioxygenase on tryptophan metabolites

Vitamin B-6 deficiency is associated with impaired tryptophan metabolism because of the coenzyme role of pyridoxal 5'-phosphate (PLP) for kynureninase and kynurenine aminotransferase. To investigate the underlying mechanism, we developed a mathematical model of tryptophan metabolism via the kynurenine pathway. The model includes mammalian data on enzyme kinetics and tryptophan transport from the intestinal lumen to liver, muscle, and brain. Regulatory mechanisms and inhibition of relevant enzymes were included. We simulated the effects of graded reduction in cellular PLP concentration, tryptophan loads and induction of tryptophan 2,3-dioxygenase (TDO) on metabolite profiles and urinary excretion. The model predictions matched experimental data and provided clarification of the response of metabolites in various extents of vitamin B-6 deficiency. We found that moderate deficiency yielded increased 3-hydroxykynurenine and a decrease in kynurenic acid and anthranilic acid. More severe deficiency also yielded an increase in kynurenine and xanthurenic acid and more pronounced effects on the other metabolites. Tryptophan load simulations with and without vitamin B-6 deficiency showed altered metabolite concentrations consistent with published data. Induction of TDO caused an increase in all metabolites, and TDO induction together with a simulated vitamin B-6 deficiency, as has been reported in oral contraceptive users, yielded increases in kynurenine, 3-hydroxykynurenine, and xanthurenic acid and decreases in kynurenic acid and anthranilic acid. These results show that the model successfully simulated tryptophan metabolism via the kynurenine pathway and can be used to complement experimental investigations.

Impact of vitamin B6 status on psychological distress in a longitudinal study of HIV-1 infection

OBJECTIVE

Inadequate vitamin B6 status has been associated with altered neuropsychiatric function, possibly through its effect on the metabolism of neurotransmitters, including serotonin (5-HT). The present eighteen month longitudinal study evaluated the relationship between vitamin B6 status and psychological distress in HIV-1 infected individuals, controlling for the influence of negative life events, social support and coping style.

METHOD

Biochemical measurements of nutritional status, and dietary intake evaluations were obtained in HIV-1 seropositive homosexual men, (at baseline: CDC Stages II and III, n = 70; Stage IVA, IVC2 n = 18) at six month intervals. Alterations in nutrient status (e.g., vitamin B6 adequate to inadequate; inadequate to adequate), were compared with changes in psychological distress, measured by the Profile of Mood States, using a multiple regression analysis.

RESULTS

A significant decline in psychological distress was demonstrated with normalization of vitamin B6 status from inadequate to adequate status (p < 0.02). A decrease in psychological distress was also observed with increased tryptophan intake in subjects who were vitamin B6 adequate (p < 0.02).

CONCLUSIONS

Significant effects for the nutritional variables remained even when negative life event stressors, social support, and coping style were controlled, suggesting that vitamin B6 status may be an important co-factor in determining level of psychological distress over time in HIV-1 infected individuals.

High-performance liquid chromatographic determination of 3-hydroxykynurenine with fluorimetric detection; comparison of preovulatory phase and postovulatory phase urinary excretion

A high-performance liquid chromatographic assay for 3-hydroxykynurenine in human urine is described. A fluorescent derivative of 3-hydroxykynurenine was prepared, based on the reaction of the compound with p-toluenesulphonyl chloride in a basic medium. The analytical method for the measurement of the fluorescent compound employed a Tosoh ODS 80 column eluted with 10 mM potassium dihydrogenphosphate (pH 4.5) and acetonitrile (3:2, v/v) and detection at an excitation wavelength of 375 nm (10 nm bandpass) and an emission wavelength of 455 nm (10 nm bandpass). The column temperature was maintained at 25 degrees C. The detection limit was 3 pmol (673 pg) at a signal-to-noise ratio of 5:1. The fluorescent derivative of 3-hydroxykynurenine was eluted at ca. 12.5 min. The technique was applied to the analysis of human urine. The total analysis time was ca. 15 min.

Effect and mechanism of action of methomyl and cypermethrin insecticides on kynurenine metabolizing enzymes of mouse liver

The effect of methomyl and cypermethrin insecticides on the B6-dependent kynurenine hydrolase (KH) and kynurenine aminotransferase (KATE) was studied. These insecticides induced pronounced inhibition on the (KH) and (KATE) enzymes after single dose treatment. Repeated doses of methomyl induced inhibition on the (KH) and (KATE) activities, whereas repeated treatment with cypermethrin had no effect on the activities of these enzymes. In vitro methomyl inhibited (KH) and (KATE) enzymes at 10(-6)M up to 10(-3)M, through a competitive mechanism. Methomyl and cypermethrin are capable of causing alterations in the kynurenine metabolizing enzymes of mouse liver.

A radioimmunoassay for phosphorylated forms of vitamin B6

Hapten-specific antibodies are found in rabbit serum afterimmunization of the animals with phosphopyridoxyl-bovine serum albumin. These were purified approximately 80-fold by salt fractionation and affinity chromatography on phosphopyridoxyl-aminoethyl cellulose. The purified hapten-specific antibodies were covalently coupled to Immunobeads. The antibody-Immunobead preparation binds [3H]pyridoxine phosphate. This provides the basis for a radioimmunoassay for vitamin B6 derivatives. [3H]Pyridoxine phosphate is displaced from the matrix-attached antibodies by pyridoxine phosphate, pyridoxamine phosphate, and pyridoxal phosphate, but is not displaced to any significant extent by pyridoxine, pyridoxamine, pyridoxal, or 5'-deoxypyridoxal. The antibody-Immunobead preparation may be recycled for reutilization in radioimmunoassay procedures. The sensitivity of the assay is in the picomole range.

Effect of leucine at different levels of pyridoxine on hepatic quinolinate phosphoribosyl transferase (EC 2.4.2.19) and leucine aminotransferase (EC 2.6.1.6) in rats

1. Effects of incorporating 30 g leucine/kg into diets on quinolinate phosphoribosyl transferase (QPRT; EC 2.4.2.19) activity and leucine aminotransferase (EC 2.6.1.6) activity were studied in groups of rats receiving 5, 30 and 60 micrograms of pyridoxine/10 g diet. 2. The results indicated that 30 g leucine/kg diet significantly reduced the QPRT activity when the diets provided 5 micrograms pyridoxine/10 g and that the effect was only marginal when the diet included 30 micrograms pyridoxine/10 g. The inhibitory effect was completely absent when the diet provided higher amounts of pyridoxine (60 microgram/10 g). 3. These results suggest that additional amounts of pyridoxine are necessary to counteract the effects of excess of leucine in the diet. 4. Leucine aminotransferase activity was increased in rats given diets containing higher amounts of pyridoxine; supplementary leucine also increased the enzyme activity.